This invention relates to the control of ink viscosity in an ink jet printhead.
In ink jet printing, it is important to control the volume and velocity of the ink drops ejected from a printhead and applied to an adjacent substrate in order to maintain constant and good image quality. This is especially important in hot melt ink jet printing in which the viscosity of the ink can change significantly with temperature changes. Conventionally, the control of ink viscosity is achieved by selecting the constituents of the ink in such a way that the ink will have a desired viscosity at a specific temperature and then controlling the temperature of the printhead so that the ink is ejected at that temperature. Despite such efforts to control ink viscosity, however, the viscosity of ink used in ink jet printheads can vary because of aging of the ink or batch-to-batch variations in the ink or variations in ink temperature from one printhead to another or from time to time in the same printhead, resulting in image quality variations.